A post I made today had a 23-Oct timestamp.
After some investigation, I determined it was because I had left the create post screen open in a firefox tab last 23-Oct, then closed my browser. On my next launch of firefox, the SessionSaver extension automatically reloaded my previous session, but the create post screen still had the 23-Oct date. I had to manually change the date.
Note to self: Refresh the create post screen always.